Assembling guide

Figure 30. Initial layout of components in yaw angle subsystem.

The first step consists of disassembling the previous structure, in order to remove those elements that are not necessary anymore and replace them with the new components.

The assembly begins at the bottom base, which supports the weight of the entire system and where it joins to the USV.

The components that must be removed before proceeding to install the new ones are the DC motor GM4632-370, as well as the communications board. The coupling of the motor to the base was formed by four M3 screws, attached to a metal clamp around the motor. The motor sits on an acrylic sheet crossed by the coupling screws, so it must also be removed. The communications board was adhered by a Velcro tape, so its removal is simple.

Figure 31. New layout for the yaw angle subsystem.

Once everything has been removed, the procedure to add the new servomotor begins.

This phase consists of the assembling of the yaw angle subsystems.

The fixing of the servomotor to the base is done by using the existing holes in its case.

To do this, the motor is oriented in such a way that its axis of rotation is parallel to the vertical axis of the structure. The problem is that the back part of the case is not com-pletely flat, as it contains a bulge. Said protuberance has the purpose of carrying out a hooking point for different brackets depending of the use of the servomotor.

Because of this, it is necessary to make an incision in the base to accommodate it. A first attempt was made, shown in the red box of figure 31. However, this attempt failed due to the use of inadequate tools. Finally, it was made again in another position (blue box), this time making a single hole to house the extreme of the shaft, instead of trying to reduce the entire surface, and then make 6 through holes to insert the screws.

The screws were initially planned to use M2.5. Nonetheless, making this type of holes on the base resulted in an arduous and complicated work due to the available tools, so in the end the solution taken was to make larger holes, finally being 3.5 mm of diameter

to house M3 screws. This modification necessitated widening the holes in the servo housing using a hand drill at low rpm to prevent from damaging the servo.

Figure 32. Locking the servo in its place on the surface of the base.

Once the servo is fixed, the next step was to adapt the height of the assembly due to the larger size of the motor. Initially, the solution proposed was to reduce the height of the gear. This option was quickly discarded during the assembly phase due to the difficulty of said operation. As the height of the gear cannot be reduced, it is decided to increase the height of the assembly, by adding a seat made in acrylic panel for the cylindrical block thus compensating for the increase in height of the servomotor, as it can be seen in the green box of the figure 32.

The connection between the shaft and the driver pulley is made by inserting a pin of 3 mm in diameter, to ensure the joint movement of the gear and the motor.

Figure 33. Pin insertion through both gear and shaft

Figure 34. Antenna supports locked in place showing the old set of holes.

Figure 34 shows the modifications to the upper base.

On the one hand, it is necessary to make new holes to fix the supports the base. These holes have the same relative arrangement as those holes drilled previously, but at a shorter distance from the centre of the base as it can be seen in the right part in figure 34. The diameter of these holes is 7 mm, to facilitate the introduction of the bolts. The union is made with M6 bolts with hexagonal head. It ends with the use of nut and washer set and thus fix the union properly.

On the other hand, the hexagonal block of the lower gear set is fixed to the base by using other six M6 hexagonal head bolts. In figure 34 it can be seen how there are two different sets of holes in the central part, six holes forming an inner hexagon and other six forming an outer hexagon. The reason for this is that the cylindrical block previously used in this structure is replaced by one used on a homologous system. However, although both blocks have the same purpose and same dimensions, they vary in some of the manu-facturing materials, as well as the exact arrangement of the union holes.

The six holes of the inner crown correspond to the block previously used, while those belonging to the outer crown are those to the block that is going to be used in this occa-sion.

Figure 35. Bearing and its housing assembling.

The next step is to mount the synchronous belt.

First, the 10 mm diameter bearing that is located in the driven part of the transmission has to be placed. To do this, the bearing is fitted into its housing, and once this is done, the bearing is inserted into the upper hole of the support. The position is fixed by the 4 holes in the housing.

To do this, it is necessary to make holes in the support to allow the passage of screws.

The holes are marked by using a pointer, which leaves a pressure mark to guide the holes. Then, a vertical drill is used to make the drills. The use of the vertical drill is rec-ommended because the antenna supports are made of aluminium, so the additional power compared to the hand drill is suitable.

Finally, M3 bolts are introduced, and these are fixed in place thanks to the joint use of nut and washer of the same metric, with which the assembly is locked in the proper position. The result can be seen in Figure 35.

This same procedure is repeated later on the other antenna support, for the dragged set of components that allow the pitch rotation.

Figure 36. Locking the servomotor in the antenna support.

Next, the servomotor is fixed to the support at the desired height to satisfy the tension needs for the belt. To position the servo in place the holes in the case are used as in a similar way to the previous motor. Once again, it is necessary to enlarge said holes to accommodate M3 bolts. However, the reason for this change is different from the previ-ous case, since the problem lies in that there was no availability to acquire screws from the original metric (M2.5) with enough length, while there was availability for wider and longer screws.

Initially, it was planned to use 6 screws according to the design. Nevertheless, due to the layout of the case, the lower holes are left free, as the use of nut-screw assembly become an impossible task due to the proximity of the electric connections of the servo.

A final modification from the computer design was performed in the central hole of the fixing counterpart element. Due to the precise adjustment between the shaft and the hole, the rotation of the shaft is impeded by the friction produced against the wall of the opening. By using the hand drill, the said hole is widened as it is shown in the figure 37

Figure 37. In detail view of the widening of the hole allowing free rotation of the shaft.

Next, the shaft of the driven part is introduced into the bearing, in order to prepare the pulleys' addiction.

The fixing of the pulleys uses the same principle used in the yaw gear system. A hole is made in the hub of the pulleys, in which a pin is then inserted, which exerts the necessary pressure on the shaft so that both elements rotate together.

Once the pulleys are inserted and fixed, the driver shaft is closed by adding its bearing, as well as fixing the housing of this bearing to the bracket support. To finish the assembly of the timing belt, the bracket is fixed to the antenna support four M3 screws.

Figure 38. Synchronous belt assembled.

The antenna is mounted on two metal plaques. These plates are attached to the shafts in charge of its movement, these being the driven shaft of the belt, and the dragged shaft that follows the rotation.

The union between the shafts and the plaques are made with eight screws. The shaft that is part of the transmission belt is made of aluminium, and these holes contain the thread directly, so it is not necessary to use nuts to retain the screw, it goes directly threaded to the hole.

The second shaft is manufactured by 3D printing. This method allows great flexibility when it comes to obtaining the piece, however it does not have the enough precision nor

enough resistance to make the thread directly in the hole, so this side is fixed according to a screw-nut union.

Figure 39. On the left, the driven shaft fixed to one plaque. On the right, the other plaque, dragged shaft and union elements.

To conclude the assembly, the antenna is attached to both metal plaques, by using four M6 screws, two for each plaque. The holes in the antenna are threaded, the union is done by just threading the screws in the holes.

Figure 40. Assembly of the directional antenna completed.

6. DESIGN OF THE ACTUATION CONTROL FOR